Excitonic topology and quantum geometry in organic semiconductors

TL;DR

This paper reveals that excitons in organic semiconductors can have topologically non-trivial states protected by symmetry, controllable via strain and chemical modifications, with implications for future optoelectronic devices.

Contribution

It introduces the concept of excitonic topological phases in organic semiconductors and demonstrates their controllability and geometric properties, bridging excitonic physics and topological materials.

Findings

Identification of topologically non-trivial excitonic states in organic semiconductors

Control of excitonic topology through strain and chemical functionalisation

Prediction of lower bounds on excitonic spatial spread based on quantum geometry

Abstract

Excitons drive the optoelectronic properties of organic semiconductors which underpin devices including solar cells and light-emitting diodes. Here we show that excitons can exhibit topologically non-trivial states protected by inversion symmetry and identify a family of organic semiconductors realising the predicted excitonic topological phases. We also demonstrate that the topological phase can be controlled through experimentally realisable strains and chemical functionalisation of the material. Appealing to quantum Riemannian geometry, we predict that topologically non-trivial excitons have a lower bound on their centre-of-mass spatial spread, which can significantly exceed the size of a unit cell. Furthermore, we show that the dielectric environment allows control over the excitonic quantum geometry. The discovery of excitonic topology and excitonic Riemannian geometry in organic materials brings together two mature fields and suggests many new possibilities for a range of future optoelectronic applications.